Water purifiers are hitherto known that have a plurality of filter tanks as disclosed in JP 8-84989 A (PTL 1). A hollow fiber membrane water purifier disclosed in JP 8-84989 A (PTL 1) has hollow fiber membrane filters that are contained in respective filter tanks. Dirty raw water flowing into the filter tanks are purified by passing through these filters.
In a water purifier disclosed in JP 8-84989 A (PTL 1), water purified by passing through one filter or filters of one or more filter tanks washes a filter in a further filter tank.
A water purifier disclosed in JP 8-84989 A (PTL 1) has a plurality of electromagnetic valves for switching between a channel through which water passes through a first filter tank and a channel through which water passes through a second filter tank. The opening and closing of these electromagnetic valves is electronically or electromagnetically controlled by a controller.
The channel through which water passes through the first filter tank is intended to be used for, for example, producing purified water in a liquid purification device. The channel through which water passes through the second filter tank is intended to be used for, for example, backwashing the filter in the first filter tank in the liquid purification device.